Method of pulping cellulosic substances



June 5, 1962 l A. M. THoMsEN 3,037,901

METHOD OF PULPING CELLULOSIC SUBSTANCES Filed April 16, 1959 FMH AS.IL/1m? Y GA J VAPUES INV ENTOR.

States In general, when the term pulp is used in connection withcellulose the inference is that the subject discussed is to producesomething suited to paper making. Contrariwise, the field in which thisprocess ybelongs is in the culture of micro-organisms, so the object ofmy Work is to produce a pulp suited to conversion into sugars, thealmost universal food for such micro-organisms as have an economicstatus.

It is also an object of my process to obtain, in some commercial form,various other derivatives of the noncellulose portion of the cellulosicraw material on which I operate and thus to cheapen the cost of theentire operation. The character of such material is most varied. Itcould, of course, be high grade wood, but the lowest form of thatmixture of bark and saw-dust which is the ultimate end of the combinedlumber and paper mill will be equally acceptable. Virtually anycollected vegetable waste, such as sugar cane bagasse, lit only for fuelis however my prime objective. On such woody material the cellulosefraction will be more than half, while methanol, acetone and a low-ashcarbon will represent the non-cellulose portion.

My pulping agent is the normal ammonium sulphite. I am aware that theconventional sulphite pulping with an ammonia base, instead of lime,soda or magnesia, is old and produces an excellent pulp for papermaking. This version is, however, entirely different. Presumably this isdue to the higher temperature employed, something that in conventionalpractice would result in a burned cook. I rind it necessary with mysulphite operation to reach a temperature approximately 375 F., whichcorresponds to a gage pressure of 175 pounds. temperature there is nosign of carbonization but a rapid pulping action, but the liberatedcellulose has but little strength and is uniit for paper making. Thisvery attack on the liber itself is a gain in my next step, that ofsacchariication, shortening the time and thus increasing the yield ofsugar. Variations in my process is virtually confined to minoradjustments as to temperature and time, so I will call the steps setforth on the drawing as representing my preferred version. In thusexplaining said drawing I will, therefore, have fully described myprocess and I will give at the same time full instructions for theoperation so that any one familiar with the language of pulping canduplicate my work.

At the top of the drawing I have shown a feeder which is merely anold-fashioned acid egg worked with steam. In this device I commingle thecellulosic material with cooking liquor and with some re-cycled spentcooking liquor. Of course, the raw material must be in a suitable stateof division. I employ approximately 40% of the Weight of the rawmaterial in ammonium sulphite and then turn on steam. It is of course toadvantage that all material be preheated. When the pressure in the eggexceeds that in the digester the valve between both is opened and thecharge in the egg is projected into the digester where no extra steam isneeded. From the digester the pulped material ows continuously into theblowpit, with attendant evolution of steam, through a nozzle type ofdischarge opening.

'I'he diameter of said nozzle and the volume in the digester are soproportioned that the time of residence in the digester at approximately175 pounds gage pressure shall be enough for complete pulping. Thisdepends At this.

arent Mice largely upon the type of raw material processed, say 2 hours,more or less as may be found advantageous by -actual performance. As thecharge from the egg is in super-heated condition with reference to thedigester no steam and no circulation is needed or desired in thisdevice.

In the blowpit separation is made between the pulp, which is now readyfor saccharication, and the spent liquor. to the feeder and the densityof the 4accepted fraction passed on the evaporator is increased thereby.A convenient source of steam for the evaporator is the lowpressure steamcontinuously evolved from the digester discharge.

After evaporation to a density of approximately 50% solids, thisconcentrated liquor is absorbed in the pores of a pre-formed spentliquor coke which is, in part, ref The car-` cycled from a subsequentcarbonizing stage. bonizer may be an outside heated retort or a Staffordtype with inside heating in the shape of circulated, reheated gas. Ineither case a mixture of gas and vapors is evolved and coke remains.This coke is, in part, recycled to the absorber as previously describedand in part constitutes an accepted fraction. It is very low in ash andwell suited for many purposes. Most of this ash will, in general, -beremoved if said coke be washed with a solution of sulphur dioxide inwater, and the dissolved calcium bi-sulphite can then be neutralizedwith ammonia, the calcium separated and the ammonium sulphite added tothe cooking liquor to make up for unavoidable losses. It forms avaluable by-product and, of course, avoids any waste liquor disposalproblem.

The gas and vapors leaving the carbonizer is next sent to ascrubber-condenser, i.e., a Vessel in which cooling is effected by aliquid spray, said liquid passing through a cooler before being usedonce more as a spray. From this device, only a fuel gas should emerge inaddition to the re-cycling liquid which, of course, is augmented involume by the condensed liquids yielded by the gas and vapors from thecarbonizer.

Inasmuch as ammonium sulphite is not quite stable at temperatures nearboiling, I have shown some recoveries of such volatilized material fromboth the blowpit and from the evaporator. All such material becomes,ultimately, a part of the regenerated cooking liquor and to this I nowadd a part of this condensate obtained from said scrubber-condenser.However, as non-volatile arnmoniu-m compounds are also formed in thedigestion I send a part of said condensate through a still with theaddition of enough lime to decompose all such ammonia salts, theresulting gas and vapors going to a mixing chamber near the bottom ofthe drawing. The still thus gives two products, said volatile materialand a slurry composed of insoluble calcium salts and a solution ofsoluble calcium salts.

`In the event that said slurry contains enough calcium sulphide tojustify the operation I have shown it entering into a carbonator whereit is commingled with carbon dioxide, setting -free such residentsulphur as hydrogen sulphide. Such gas is, in turn, burned and theresulting sulphur dioxide sent to the mixing chamber. I have then shownsaid device as yielding the re-cycled mother liquor and some volatilizedmaterial which passes to a condenser. The condensed material is chieflymethanol but some acetone is also present, as well as some ammonia saltsin solution. The latter is, of course, re-cycled and the former refinedfor the market. Collectively, they .represent a derivative from themethoxyl content of the raw material.

This narrative, in conjunction with the drawing, Will enable anyonefamiliar with conventional pulp operations and such additional mattersas ammonia distillation and As much of this as possible is re-cycleddirect charcoal making to operate my process. Subsequent Vrenernentswill, of course, only be possible after such a person has had someexperience with the specific method herein disclosed.

Having thus fully described my process, I claim:

1. The method of pulping cellulosic material with a cooking liquor thatconsists essentially of normal ammonium sulphite which comprises;commingling said cellulosic material with a solution of ammoniumsulphite and digesting same at the approximate temperature 375 F. until`Said material shall consist essentially of cellulose bers andspent'cooking liquor; separating said cellulose yfrom said spent cookingliquor; evaporating the cooking liquor and absorbing the concentratedmaterial in a preformed, recycled spent liquor coke; carbonizing theresultant liquor-saturated coke to obtain coke for recycling, coke as anaccepted product, and volatile substances;

condensing said volatiles to produce liquid and gaseousV of cellulosebers and spent cooking liquor issuing continuously from thecontiningtvessel in4 which said diges- Ition takes place, essentially inthe form of a jet with simultaneous evolution of steam, said ste-ambeing thereafter utilized in the evaporation of spent liquor.

3. The method of pulping cellulosic material set forth in claim 1, withthe added step that a portion of the condensed liquid products fromcarbonizing be commingled with lime and heated to decdinpose residentnon-volatile salts of ammonia, the ammonia thus volatilized beingafterwards absorbed in and becoming a part of the regenerated cookingliquor. l

4. The method of pulping cellulosic material set forth in claim 1, withthe added step that the accepted cokefraction produced therein be'further refined by leaching same With a Water solution of sulphurdioxide, the lime salts thus solubilized as calcium bi-sulphite beingfreed from calcium by precipitation with ammonia, the resulting ammoniumsulphite being re-cycled as a component of the regenerated cookingliquor.

References Cited in the tile of this patent UNITED STATES PATENTS 201,315,889 Westin sept. 9, 1919 2,739,039 IPhelps Mar. 20, 1956 2,752,243Barton June 26, 1956 FOREIGN PATENTS 139,168 Y Great Britain Apr. 14,1921 OTHER REFERENCES Hausen: Alkalis as Bases for Sulte Liquor, TAPPI,

Series X, June `1927, pages 130-139.

1. THE METHOD OF PULPING CELLULOSIC MATERIAL WITH A COOKING LIQUOR THATCONSISTS ESSENTIALLY OF NORMAL AMMONIUM SULPHITE WHICH COMPRISES;COMMINGLING SAID CELLUOSIC MATERIAL WITH A SOLUTION OF AMMONIUM SULPHITEAND DIGESTING SAME AT THE APPROXIMATE TEMPERATURE 375* F. UNTIL SAIDMATERIAL SHALL CONSIST ESSENTIALLY OF CELLULOSE FIBERS AND SPENT COOKINGLIQUOR; SEPARATING SAID CELLULOSE FROM SAID SPENT COOKING LIQUOR;EVAPORATING THE COOKING LIQUOR AND ABSORBING THE CONCENTRATED MATERIALIN A PREFORMED RECYCLED SPENT LIQUOR COKE; CARBONIZING THE RESULTANTLIQUOR-SATURATED COKE TO OBTAIN COKE FOR RECYCLING, COKE AS AN ACCEPTEDPRODUCT, AND VOLATILE SUBSTANCES; CONDENSING SAID VOLATILES TO PRODUCELIQUID AND GASEOUS PRODUCTS; SEPARATING SAID LIQUID PRODUCTS INTO ASOLUTION OF AMMONIUM SALTS AND METHOXYL DEGRADATION PRODUCTS; ANDRECYCLING SAID SOLUTION OF AMMONIUM SALTS AS A REGENERATED COOKINGLIQUOR.